Motor-control system.



A. H. ARMSTRONG.

MOTOR CONTROL SYSTEM.

APPLICATION FILED JULY 21, 1906.

91 9,302, I Patented Apr. 27,1909.

Fig. 2.

Invent or I7T I bert. H. firmstrong.

UNlTED @IATEh ill hllfihl.

ALBERT H. ARMSTRONG, F SCHENEOTADY, YORK, ASSIGNOR T0 GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

Specification of Letters Patent.

?atented April 27, race.

To all whom it may concern:

Be it: known that l, ALBERT ARM- STRONG, a citizen of the United States,residing at Schenectady, county of Schenectady, State of New York, haveinvented certain new and useful improvements in Motor- (ontrol Systems,of which the following is a specification.

The present invention has for its object to improve the control ofelectric motors, and particularly motors which are adapted to i'etulrnenergy to the line when drivenby the car 4 In electric railway systems,for example, it is necessary to provide means for operating motors atvarious s ds, and it is also ad: vantageous to be ablie io cause themotors to operate as braking generators, and as such to return energy tothe line in going down grade or upon slowing down the train. inalternating current systems, induction motors can be used to advantageas the. propelling motors for the car or locomotive, but

7 since these motors must run at a definite speed determined by thefrequency of the car or locomotive is traveling at such a high speed asto drive them above synchronism.

By my invention, means are provided whereby motors of the characterdescribed, and other motors which run at synchronous speeds, may becontrolled so as to give va riat-ion of speed within any desired limitsand may be made to return energy to the line irrespective of the s ecdat which the car or locomotive is trave ing. To this end, I insertbetween the source of supply and the propelling motors a motor-generatorset, the generator supplying current to the propelling motor: andprovide means for varying the frequency of the current supplied by thegenerator within such limits as may be desired under any given conditionof service. In

this system, therefore, the motor-generator runs at a substantiallyconstant speed, which is slightly below synchronism when the pr0-polling motors are driving the car or locomotive, and, since the speedof the propelling motors is determined by the frequency of the currentderived from the motor-generator, a

variation in that frequency produces a like variation in the speed ofthe propelling moi tors. When it is desired to return energy to theline, the frequency of the generated current is made such that the speedof the propelling motors corresponding thereto is less than the speed atwhich they are driven by the car or locomotive, whereupon the repellingmotors, being driven above synchronism y the load, act as generators andsupply energy to' the generator oi the motorgenerator set. Thisgenerator new acts as a motor and drives the motor of the motorgeneratorat a speed slightly above synchronism, causing it to return energy tothe source. The frequency of the generator is varied without making anychange in the generator itself, preferably by exciting its field withcurrent from a small variable speed motor-generator set, this excitingcurrent having a frequency depending on the speed of the set.

My invention will be more fully understood and its objects and advantaes will be more clearly apparent from the fa owing detailed description,while its scope Will be seen from the ap ended claims.

Int e accompanying drawing, Figure 3 indicates diagrammatically a singlecar or locomotive equipment arranged in accordance with the presentinvention; and Fig. 2 shows a car having installed thereon the apparatusindicated in Fi 1.

Reference being had to the drawing-M and M are tvro propelling motors,indicated as multihose induction motors, but which may be single-phaseinduction motors or the other motors having synchronous speeds.

L is a source of current supply indicated as a trolley-wire or thirdrail and a ground return.

A is a motor-generator, the motor 1 of which in connected to the sourceof sugpfy by means of a current collector T. i connection may be adirect one, but if the line potential is high, a ste lOWTl transformer'l may be introducer. The transmission is shoe-n as being single-phase,the motor 1 being therefore also of a sin lephase type, but it will ofcourse be un erstood that multi-phase transmission lines and multiphasemotors for the motor-generators may be employed. The armature ofenerator 2 is connected to the motors M 1 an M? A reversing switch R maybe ar- 1 ranged in the connection between the gen" erator'armature andmotors M and M in order that the direction of rotation of the motorsand, therefore, the direction of travel of the car or train, may bechanged.

B is a small variable-speed motor-generator for exciting the field ofthe main generator. Motor 3 of the auxiliary set may conveniently be ofthe series commutating type receiving current through a compensator ortransformer T C is a controller for connecting the terminals of themotor 3 across variable poitions of the transformer or compensator, thespeed of this motor, of course, varying with t e im ressed voltage,since the load is substantia y constant. The field of the auxiliarygenerator is excited from a source of direct current, as for example,storage battery S. A rheostat U is placed in the field cirruit of theauxiliary generator with a switch V which may be used to open the fieldcircuit, and also to alter the amount of resistance in thiscircuit.

In starting, or when it is desired to run the caror train at its lowestspeed, the main switch W is closed, the reversing switch is moved to theroper running position, and the controller 8 is brou ht to the firstrunning position, switch {7 being left open; bot motor-generator setsnow begin to operate, the main set A at its fixed speed determined bythe constant frequency of the source, and the auxiliary set at itsvlowest speed. Controller 0 is then moved through its various runningpositions until the auxiliary set is runnin speed. Switch V in the fieldcircuit of the auxiliary generator 4 is then closed. Since the auxiliarygenerator is running at its highest speed, the frequency of. the currentemanatin therefrom is also high, and therefore the field of the maingenerator is enerized by current having a high frequency.

hen the frequency of the exciting current for the main generator is atits highest value, the frequencyot the current supplied by its eneratorto the propelling motors, is at the fewest value, and, since this latterfrequency determines the speed of the motors M and M these motors propelthe car or locomotive at a slow 5 eed. By moving the main controllerbac: into its different running'positions, the speed of the motor 3 isreduced and the frequency of the current supplied b the auxiliarygenerator is decreased. Therefore, it follows that the frequency or" thecurrent supplied by the main generator to the propelling motors, andconsequently the speed at which motors M and M must run, is alsoincreased. It will be seen that by providing a large number of runningoints on the controller C, wide variations in the speed of the motorsmay be obtained,

at its highest l ary generator, and therefore the out-put of the maingenerator and the power of motors M and M may be controlled.

Since the synchronous speed of motors M and M may be varied within widelimits, and since these motors will 0 erate as braking generators whendriven y the load at a speed'slightly above synchronous speed, a verysimple and convenient regeneratwe system is provided, for it is onlynecessary, in order to make the motors act as braking generators, to soadjust the controller 0 as to make the frequency of the main generatorssuch that the motors are left running at a s eed slightly abovesynchronous' Under t ese conditions the motors operate as generatorsdriven by the load and supply current to the main generator which nowacts as a motor and drives the motor 1 above synchronism, causing it toreturn energy to the.

so as to keep the synchronous speed of the motors below actual speed.Thus, as long as the car or train is traveling, at a rate correspondingto an speed ofthe motor above the 1 lowest speed o tainable, it ispossible to produce an electrical brakingiaction.

Although I have described in detail a preferred form of my invention andthe best instrumentalities known to me for carrying it out, I do notdesireto be limited to the particular form shown or the instrumentahtiesemployed, since in its broader aspects, my invention covers other formsand instrumentalities in addition to those shown and described.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is,-

1. The method ofoperating an induction motor as a braking generatordriven by the load and returning energy to a source of current ofconstant frequency, which consists in interposing between the motor andthe source a motor-generator the motor field of which is excited by analternating current, and then varying the frequency of said excitingcurrent in accordance with variations in the speed of the brakinggenerator.

2. In combination, a source of current, a motor whose speed is governedby the frequency of the current supplied thereto, a motor-generatorincluding a motor connected to said source and an alternating currentgen erator having its armature connected electrically to the first-11aled motor, and means for varying the fre uency of the exciting cur rentfor the field di said generator. v

3. In combinatioma source of current, a motor whose speed is governed bythe frequency of the current supplied thereto, a1notor-generatorincluding a motor connected to said source and a separatelyexcitedgenerator-whose armature is electrically connected to saidfirst-named motor, and means for llfl ing current generator having itsarmature connected electrically to the first-named motor and having aseparately excited field, and

, means for varying the frequency of the ex- I .citin' current for saidfield.

5. n combination, a source of alternating j current, a-motor Whose speedis governed by 1 the frequency of the current supplied thereto, amotor-generator including a constants eed motor connected to said sourceand an a ternating current generator having its arcited alternatingcurrent generator having its armature connected to the first-namedcurrent distribution system, a vehicle having including a constant-speedmotor connected citing current for said generator.

- a motor-generator including a motor con- .speeds to cause theexcitation of the main l mature connected to said first-named motor, 1and means for varying the frequency of the exciting current for saidgenerator. I 6. In combination, a source of alternatirg currenthaving afixed frequency, a motor l whose speed is governed by the frequency ofthe current supplied thereto, a motor-generator including aconstant-speed motor connected to said source and a separately exmotor,and means for varying the frequency of the exciting current for saidgenerator.

7. In, an e ectric railway, an alternating a propelling motonwhose speedis governed by the frequency of the current sup lied thereto, amotor-generator on said ve icle to said distribution system and analternating current generator having its armature connected to thefirst-named motor, and means for varying the frequency of the ex- 8. Incombination, a source of alternating current having a constantfrequency, a motor or'motors whose speed is overned by the frequency ofthe current supplied thereto,

nected to the source and an alternating current enerator having itsarmature connecte to said motor or motors, an alternating currentgenerator for exciting the field of the other generator, and means forvarying the frequency of the current supplied by the exciting enerator.

9. In com ination, a source of alternating current having a constantfrequency, a motor or motors whose speed is governed by the frequency ofthe current supplied thereto, a motor-generator including a motorconnected to said source and an alternating current generator connectedto said motor or motors, an auxiliary generator for exciting the maingenerator, and a variable speed motor for riving said auxiliarygenerator at various generator connected to said motor or motors,

an auxiliary motor-generator lncluding a variable speed motor, and agenerator for ;exciting the main generator with currcnt varying infrequency, and a controller for varying the speed of the motor of theauxiliary motor-generator to cause variation in the frequency of theexciting current delivered by said auxiliary generator.

11. In combination, a source of current, a motor whose speed is governedby the frequency of the current supplied thereto, a

, motor-generator including a motor connected to said source and analternating current generator having its armature connected electricallyto the first-named motor, and means for varying the frequency and thestrength of the exciting current for the field of said generator.

12. In combination, a source of current, a motor Whose speed is governedby the frequency of the current supplied thereto, a motor-generatorincluding a constant-s eed motor connected to said source and an aternating current generator having its armature connected electricallyto the firstnamed motor and having a separately excited field, and meansfor varying the frequency and the strength of the exciting current forsaid field.

13. In combination, a source of alternating current having a fixedfrequency, a motorwhose speed is governedby the frequency of the currentsupplied thereto, a motor-generator including a constant-speed motorconnected to said source and a separately excited alternating currentgenerator havin its armature connected to the first-name motor, andmeans for varying the frequency and the stren th of the excitingcurrent.

14. In com ination, a source of alternating current having a constantfrequency, a motor or motors Whose speed is overned by the frequency ofthe current siipp ied thereto, a motor-generator including a motorconnected to the source and an alternating current generator having itsarmature connected to said motor or motors, an alternating c-urto, amotor-generator including a motor connected to said source and analternating current generator connected to said motor or motors, anauxiliary motor-generator including'a variable speed motor and aenerator for exciting the main generator wit current varying infrequency, a controller for varying the speed of the motor of theauxiliary motor-generator to cause variation in the nected to saidsource and an alternating current-generator connected to said motor ormotors, an auxiliary generator for exciting the main generator, meansfor varying the field strength of said auxiliary generator, and avariable speed motor for driving said auxiliary generator at variousspeeds to cause the excitation of the main generator to erases beeffected by the current of variable frequency. i

17. In combination a sourceof alternating current having a fixedfrequency, a niotor or motors Whose speed is governed by the frequencyof the current supplied thereto, a motor-generator including a motorconnected to said source and an alternating current generator connectedto said motor or motors, an'auxiliary generator for exciting the maingenerator, a source of direct current for excitin the field of theauxiliary 'enerator, a

control er for varyin the strengtn of the exl generator,

citing current for t is auxiliar and a variable speed motor for drivingsaid auxiliary generator at. various speeds to cause the excitation ofthe main generator to beefiected by currents of variable frequency. InWitness whereof, I have hereunto set my hand this 19th day of July,1906.

ALBERT H. ARMSTRONG.

witnessesz I I BENJAMIN B. HULL, HELEN ORFORD

